Inching valve

Abstract

An "inching" valve for use in vehicles such as an industrial lift truck for controlling the operation of separate pressurized fluid actuated clutches for driving the vehicle forwards or backwards wherein rotary and axial movements of a single cylindrical valve piston within its cylinder control respectively clutch selection for forward or reverse drive and the "inching" movement in the drive direction selected in functional relation with actuation of the brake pedal.

I claim: 
     
       1. A combined forward, rearward and inching valve structure for controlling a motorized vehicle provided with braking means comprising a cylinder, a cylindrical piston valve member located within said cylinder and which is capable of both an axial sliding movement and also a rotational movement about the cylinder axis between two limit positions, said cylinder being provided with circumferentially spaced first and second outlet ports leading respectively to forward and rearward fluid pressurized clutch means to effect forward or rearward movement of the vehicle, a hollow forward-rearward select shaft rotatably mounted in said cylinder and on which said piston valve is mounted for rotation between said limit positions, an inching shaft mounted for axial sliding movement within said hollow select shaft, means coupling said inching shaft with said piston valve member for effecting axial movement of said valve member upon axial movement of said inching shaft, means coupling said inching shaft to the brake operating means of said vehicle, a pressurized fluid source, conduit means connecting said pressurized fluid source to an inlet port on said cylinder leading to fluid distributing passages provided on said piston valve by which the pressurized fluid is led to a selected one of said outlet ports upon axial movement of said piston valve in response to movement of said inching shaft in the brake releasing direction, a piston controlled fluid pressure regulating chamber provided within said cylinder, conduit means interconnecting said pressure regulating chamber with the conduit means leading to said inlet port, and means controlling movement of the piston in said fluid pressure regulating chamber in accordance with movement of said inching shaft in the brake releasing direction to effect a progressive increase in fluid pressure in said pressure regulating chamber thereby to effect a progressive increase in pressure of the fluid being conducted to the selected clutch means which results in inching movement of the vehicle. 
     
     
       2. A valve structure as defined in claim 1 wherein said means for controlling the movement of said piston in said fluid pressure regulating chamber in accordance with the movement of said inching shaft comprises an inching compression spring seated in a longitudinally extending recess provided in said inching shaft, said piston includes a plunger component slidable within said recess and engageable with one end of said compression spring, and a counteracting compression spring engaged with said piston for effecting a following movement of said piston in the direction to decrease the volume in said pressure regulating chamber as said inching shaft is moved in the brake releasing direction.